The present invention relates to a disc-shaped information carrier produced by means of thermoplastic deformation. The information carrier is used for the atorage of audio and video signals which are to be scanned in accordance with the pressure scanning method.
A system for pressure scanning signals, including television signals, from an information carrier is disclosed in U.S. Pat. No. 3,652,809 granted Mar. 28, 1972 to Dickopp et al. Also, a signal playback system including a record carrier with mechanical deformations which are mechanically scanned by a pickup and converted to electrical signals is described in German Offenlegungsschrift No. 25 25 369. In this latter system, the angle of inclination of the pickup with respect to the record carrier is modulated in accordance with the mechanically recorded signal thereby requiring a record carrier which is absolutely rigid. Moreover, this scanning system requires a pickup which is movable about its transverse axis so as to be able to follow the raised portions in the record with a tilting mevement.
It is known to fabricate information carriers having high storage density from flexible hard polyvinyl chloride foils. German Patent Application No. P 25 40 654 discloses an improvement in such carriers for use with the mechanical pressure scanning method by making them of a homopolymer in a stamping process and then rotating the carrier in the form of a flexible foil on a cushion of air. The cushion of air with its special saddle plate compensates for unavoidable unevennesses in the stamped foil during rotation thereby reducing the wobble of the rotating foil against the pickup.
Information carriers according to U.S. Pat. No. 3,652,809 are played back at 1500 rpm. With a groove width of 3.6 microns and a disc diameter of 21 cm, they permit storage of a video program having a duration of up to 10 minutes. Due to the precision obtained during stamping of the recording grooves or relief, this arrangement produces a satisfactory and useful signal in the pickup. However, with further reduction of the relief dimensions, no precise reproduction is possible with conventional materials and the pickup no longer produces an acceptable signal.
In order to reduce friction during playback, the stamped carrier can be coated as taught in German Offenlegungsschrift No. 2 545 445. However, the length of time during which such coatings remain effective is not entirely satisfactory and complicated and difficult production technology is required. The difficulties increase with decreasing relief dimensions since "flattening" of the stamped relief can result in loss of pulses.
It is an object of the invention to provide conditions for an extended playing period of the information carrier without having to increase its diameter. This requires reduction of the playback speed and the groove width; i.e. reduction of the relief dimensions.
It is a further object of the invention to provide a material which permits the reduced relief dimensions to be shaped with precision and which keeps the sliding friction between the pickup and the disc surface at a constant low level.